1. Field of the Invention
The present invention relates to an evaluation apparatus of a lens unit used at the time of the assembly of lens units such as a lens for cameras, an image pick-up unit and the like.
2. Description of the Related Art
Using FIGS. 1, 2, and 3., an optical axis adjusting apparatus will be explained. FIG. 1 is an outline block diagram of the optical axis adjusting apparatus. FIG. 2 is a diagram about image forming of the optical axis adjusting apparatus. FIG. 3 is a diagram showing an image in a CCD camera image-receiving surface of the optical axis adjusting apparatus.
In FIG. 1, an optical axis adjusting apparatus of a lens unit is equipped with a light source 50, a pinhole plate 51 arranged at the left of the light source 50 which has a pinhole with diameter (φ about 0.6 μm) formed by pinhole processing, a ND filter 52 and a collimator lens 53 which are arranged at the left of the pinhole plate 51, and a mirror 54 arranged at the left of these.
In the lower part of the mirror 54 in FIG. 1, a chart 55 that is opaque and plate like shape is arranged. This chart 55 is arranged so that a surface of the chart 55 may become perpendicular to an optical axis of the light that enters to the chart 55.
On this chart 55 as shown in FIG. 2, a center point (M0) of the chart 55 and eight points (M1-M8) which are located in a line at equal intervals on a ring band, a center of which is the M0 are arranged. The pinhole processing has been carried out to each point of M1-M8.
In FIG. 1, an object lens system T is arranged under the chart 55. an object lens system T has a lens system 56, a lens holding frame 57 for fixing the lens system 56, an attachment portion 58 at a main body side to which this lens holding frame 57 is inserted, a lens system 59 which is an object of adjustment arranged at the upper part of the lens holding frame 57, and an adjustment jig 8 arranged so as to contact with the lens system 9,
In an arbitrary position at the lower part of the object lens system T in FIG. 1, an image surface 61 is arranged. Under the image surface 61, a microscope lens 62, a CCD camera 63, and a focusing axis 64 are arranged. A microscope lens 62 is arranged so that the optical axis may coincide with the optical axis of the object lens system T. A CCD camera 63 is arranged under the microscope lens 62. This CCD camera 63 is arranged so that the image receiving surface may become perpendicular to the optical axis of the object lens system T.
The microscope lens 62 and the CCD camera 63, and the focal axis 64 mentioned above are mounted on a X-Y table which moves by two axes 65 for rough adjustment of axis, and an image is caught in the image receiving screen of the CCD camera 63 by adjusting two axes 65 for rough adjustment of axis.
Here, an image forming by the optical axis adjusting apparatus will be explained.
The light emitted from the light source 50 becomes parallel light rays R through the pinhole plate 51, the ND filter 52, and the collimator lens 53, and then they are reflected by the mirror 54 and become parallel light rays R′ which go to a lower part from the mirror 54.
The parallel light rays R′ are interrupted by the chart 55, and they pass the center point M0 of the chart 55 and eight points (M1-M8) located in a line at equal intervals on the ring band, the center of which is the center point M0, and then a pinhole image is formed to become nine light rays. Then, the nine light rays which have passed the chart 55 passes the object lens system T, and enter to an image surface 61. At this time, since most of the quantity of parallel light rays R′ are shielded by the chart 55, only the nine pinhole images are formed on the CCD camera 63.
Here, when the optical axis of the lens system 59 ideally coincides with the optical axis of the lens system 56 and a whole optical system, in FIG. 2 a center of gravity position of irradiated points L1-L8 on the ring band obtained by light rays R1.R2, R3, R4, R5, R6, R7 and R8 which passed the lens systems 59 and 56, and an irradiated point L0 of the center obtained by the light ray R0 which passed the lens systems 59 and 56 coincides.
However, when the optical axis of the lens system 59 does not coincide with the optical axis of the lens system 56 and a whole optical system, a center of gravity position of the irradiated points L1-L8 on a ring band and a center point of the main irradiated point L0 will be shifted.
Then, in order that the center of gravity position of the irradiated points L1-L8 on the ring band and the center point of the main irradiated point L0 coincides, an optical axis adjustment using an operation processing section 66 and fine adjustment of the two axes is 69 is carried out. That is, in the operation processing section 66, by determining for the average of X coordinates XR1-XRm and Y coordinates YR1-YRm of all the picture elements of eight irradiated points which constitute the ring band except the main irradiated point 67 (refer to FIG. 3), a barycentric coordinates B (XG, YG) in the center of gravity 68 of the ring band is obtained.
Next, a deviation (XG-X0, YG-Y0) of the main coordinates A in the main irradiated point 67 (X0, Y0) and the barycentric coordinates B (XG, YG) in the center of gravity 68 of the ring band is detected as an amount of coma at the axis (Δ X, Δ Y). Then, the two axes 69 for fine adjustment is made to move slightly according to the detected amount of coma at the axis, and the optical axis adjustment is carried out by moving slightly the lens system 59 so that an amount of coma at the axis may be settled within a standard which been set, and an optical axis adjustment is carried out.
In detection of deviation of an optical axis in the first lens system (lens system 56 in FIG. 1) and the second lens system (lens system 59 in FIG. 1), a variation in detected value is a variation of the center of gravity of a main luminous flux and the center of a ring band luminous flux. It becomes variation of the coordinates of the center of gravity of the main luminous flux and of the center of a ring band luminous flux. According to the detection method mentioned here, the main coordinate of the ring band luminous flux are computed from the average of the luminous fluxes of eight points which constitute the ring band. By averaging the calculated value, the variation in the luminous fluxes of the eight points are offset, and the variation in the main coordinates becomes small compared with the variation in each luminous flux.